Method of making diamond laps



March 22, 1955 H. P. GIFFORD 2,704,705

METHOD OF MAKING DIAMOND LAPS Filed May 27, 1952 INVENTOR 4o 39 i 37 l-LPAXSONGIFFORD a M l4 BY ATTORNEY United States Patent Ofifice 2,704,705 Patented Mar. 22, 1955 METHOD OF MAKING DIAMOND LAPS Harry Paxson Gifford, Lancaster County, Pa., assignor to Hamilton Watch Company, Lancaster, Pa.

Application May 27, 1952, Serial No. 290,181

1 Claim. (Cl. 51-293) This invention relates to a method of making metal bonded diamond laps particularly of a diameter under A of an inch.

The object of the present invention is to simpliiy the existing processes of manufacturing diamond laps and to make a lap which may be refreshed many times during its life.

A further object of the present invention is to provide a method of manufacturing a metal bonded diamond lap to provide a lap which has a solid core of mixed diamond abrasive and finely divided metallic particles. The vari ous steps of the invention are diagrammatically illustrated in the several figures, in which:

Fligure 1 is illustrative of a piece of cold rolled stee Figure 2 shows the first step of reaming a longitudinal hole in the steel.

Figure 3 illustrates the second step in which the interior of the hole is lined with flux.

Figure 4, the third step and illustrates the filling of the hole with a mixture of diamond powder and metal powder.

Figure 5 shows the punch which is turned to exactly fit the drilled hole.

Figure 6 shows the initial light tamping of the mixture in the hole.

Figure 7 illustrates the sixth step in the process in which the entire assembly is hot pressed.

Figure 8 shows the elimination of the top part of the steel and the punch by sawing.

Figure 9 shows the surfacing of the steel by a grinding wheel so that the end of the abrasive is exposed.

Figure 10 shows the turning away of the metal from the sides of the abrasive.

Figure 11 shows the undercutting of that portion of the metal adjacent the abrasive to provide clearance for the lap.

Figure 12 shows the finished lap here on a straight or tapered shank.

Figure 13 illustrates a modification in which a solid metallic core is shown without abrasive around the core.

Figure 14 shows the finished product, partly in section made in the modified form.

Referring to the figures, numerical rotation, a piece of cold rolled steel shown in Figure l at 17 is drilled by a drill 18 to provide a longitudinal bore 19. This bore is made the exact size of the desired lap.

The interior of the bore 19 is coated with a flux 20 and powdered silver solder (Easy Flow Silver Solder #5, a purchased item) 21 is dropped to the bottom of the bore, after which the correct mixture 22 of diamond dust and metallic powder is poured into the bore to fill the bore approximately half full. This mixture of diamond dust and metallic powder is carefully screened for size, both for the diamond powder and for the metallic powder as this insures the coarseness or fineness of the finished product. The metallic powder may be of a number of various suitable alloys.

With the mixture 22 half filling the bore 20, a punch 23 is turned to the exact size of the bore 20 and made sufficiently long to protrude from the bore after engaging the diamond mixture. The punch 23 is tapped by a light hand hammer 24 so that the mixture 22 is compact.

The piece of cold rolled steel together with the punch and the abrasive mixture is placed on a stand 25 and subjected to light pressure from a hydraulic press 26. The abrasive mixture is brought to a temperature of approximately 1500 F. by means of a gas ring 27, and the pressure from the hydraulic press 26 is increased to approximately 70,000 pounds per square inch. This sinters the mixture of powdered metal and diamond particles and afiixes them firmly to the cold rolled steel 17. The silver solder 21 adheres to the bottom 27 of the bore binding the molten abrasive mixture to the bottom and to the sides of the bore 19, overflowing at the top to seal the punch to the cold rolled steel. The entire piece is then removed and sawed at a point just beyond the end of the abrasive mixture, leaving a small piece of the punch 29 in the bore. The entire end 30, including both the punch and the sides of the bore, is dressed by a grinding wheel 31 until the abrasive is exposed, after which the side walls 32 of the bore enclosing the abrasive are turned away to expose the abrasive material, as shown at 33. Referring to Figure 11, that portion 34 of the cold rolled steel immediately behind the abrasive is cut away to provide clearance for the lap so that the finished product will look as shown in Figure 12 with a straight shank 35 or a tapered shank 36, depending upon the chuck with which the tapered lap is to be used.

Referring to the modification shown in Figures 13 and 14, the bore has a central rod 37 extending throughout its length and the punch 38 fits around the rod to tamp the abrasive 39 in position. The process is carried out in the manner above described to form a lap 40, as shown in Figure 14, having a central solid core formed of the rod 37.

What is claimed is:

A method of making a diamond lap, consisting in boring a hole longitudinally of the steel rod of the exact diameter and twice the length of the desired abrasive portion of the lap, introducing solder into the bore thus formed and filling the bore slightly over half full with a homogeneous mixture of diamond powder and metallic powder, inserting a punch into the bore and tamping the powder, applying heat to a temperature of 1500 to fully sinter the mixture of diamond powder and metallic powder to form an abrasive section, subjecting said section to pressure 70,000 pounds per square inch while hot, removing the majority of said punch in that part of the rod which projects beyond the abrasive section, grinding the end of said rod including the punch until the abrasive section is exposed, turning the side of the bore from the abrasive section until said abrasive is exposed, and undercutting that portion of the steel rod directly connected to the abrasive section.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF MAKING A DIAMOND LAP, CONSISTING IN BORING A HOLE LONGITUDINALLY OF THE STEEL ROD OF THE EXACT DIAMETER AND TWICE THE LENGTH OF THE DESIRED ABRASIVE PORTION OF THE LAP, INTRODUCING SOLDER INTO THE BORE THUS FORMED AND FILLING THE BORE SLIGHTLY OVER HALF FULL WITH A HOMOGENEOUS MIXTURE OF DIAMOND POWDER AND METALLIC POWDER, INSERTING A PUNCH INTO THE BORE AND TAMPING THE POWDER, APPLYING HEAT TO A TEMPERATURE OF 1500* TO FULLY SINTER THE MIXTURE OF DIAMOND POWDER AND METALLIC POWDER TO FORM AN ABRASIVE SECTION, SUBJECTING SAID SECTION TO PRESSURE 70,000 POUNDS PER SQUARE INCH WHILE HOT, REMOVING THE MAJORITY OF SAID PUNCH IN THAT PART OF THE ROD WHICH PROJECTS BEYOND THE ABRASIVE SECTION, GRINDING THE END OF SAID ROD INCLUDING THE PUNCH UNTIL THE ABRASIVE SECTION IS EXPOSED, TURNING THE SIDE OF THE BORE FROM THE ABRASIVE SECTION UNTIL SAID ABRASIVE IS EXPOSED, AND UNDERCUTTING THAT PORTION OF THE STEEL ROD DIRECTLY CONNECTED TO THE ABRASIVE SECTION. 